Process for extracting mineral oil using surfactants based on butylene oxide-containing alkyl alkoxylates

A surfactant formulation comprising at least one ionic surfactant of the general formula

• R1—O-(D)n-(B)m-(A)l-XY−M+, where
• R1 is a linear or branched, saturated or unsaturated, aliphatic and/or aromatic hydrocarbon radical having 8 to 30 carbon atoms,
• A is ethyleneoxy,
• B is propyleneoxy, and
• D is butyleneoxy,
• l is from 0 to 99,
• m is from 0 to 99 and
• n is from 1 to 99,
• X is an alkyl or alkylene group having 0 to 10 carbon atoms,
• M+ is a cation, and
• Y− is selected from the group of sulfate groups, sulfonate groups, carboxylate groups and phosphate groups, where
• the A, B and D groups may be distributed randomly, alternatingly, or in the form of two, three, four or more blocks in any sequence, the sum of l+m+n is in the range from 3 to 99 and the proportion of 1,2-butylene oxide, based on the total amount of butylene oxide, is at least 80%.